a description of a still unreleased fbi video. according to those familiar with what it shows, dzhokhar tsarnaev can be seen removing his backpack at the spot where the second bomb was placed, and acting very differently from those around him when e first bomb blew up. >> this suspect took the backpack off, put it down, did not react when the first explosion went off, and then moved away from the backpack in time for the second explosion. >> federal officials say in the hours after the fbi released photos of the bombing suspects thursday night, investigators had not yet matched any names to their pictures and, in fact, did not even have the tsarnaev brothers in any terrorist data base. only after the older brother was killed in the late night shootout in watertown were agents able to check his fingerprints and put actual names to their case. fbi agents are seeking to interview all the family members and friends of the two brothers, including the wife of the older one, tamerlan. her lawyer says he is talking to federal authorities about how to proceed. matt? >> pete williams, thank you very much.